NOAO >   Observing Info >   Approved Programs >   2017A-0424

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Program Information for 2017A-0424


PI: Maxwell Pollack, U. of Wisconsin, Madison, mpollack@astro.wisc.edu
Address: Department of Astronomy, 475 N. Charter St., Madison, WI 53706 United States

CoI: Robert Mathieu, U. of Wisconsin, Madison
CoI: Benjamin Tofflemire, U. of Wisconsin, Madison
CoI: Emily Leiner, U. of Wisconsin, Madison
CoI: Erika K Carlson, U. of Wisconsin, Madison

Title: A Study of the Nonstandard Stellar Populations and Binary Populations of Open Clusters

Abstract: Nonstandard stars, such as blue stragglers (BSs) and sub-subgiants (SSGs), have been an enduring challenge for stellar evolution theory. It is now clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, sophisticated $N$-body models show that stellar dynamical processes, specifically binary encounters, play a central role in the formation of such nonstandard stars. These stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose a study to directly probe this interface through high-precision radial-velocity measurements of the nonstandard stars and the binary populations in three intermediate-age open clusters of similar richness: NGC 7789 (1.8 Gyr), NGC 2506 (2.1 Gyr), and NGC 6819 (2.5 Gyr). Notably, NGC 6819 has 33 potential BSs, NGC 2506 has 10, while NGC 7789 has at least 27. We will also gather RV data from similar targets in the old open cluster NGC 6791 (8 Gyr), and from M67 (4 Gyr), to accompany light curves from the recent Kepler K2 data release. Our observations will provide cluster membership and binary orbital properties for these BSs, as well as identify possible SSG RV members. Our observations will also measure the hard-binary fraction and frequency distributions of orbital parameters in these clusters, establishing the environmental factors that may influence nonstandard star production. These data will be the touchstones for detailed $N$-body open cluster simulations. Combining the observed populations and the theoretical models will shed light on the different BS production rates in these clusters, and ultimately the formation mechanisms of these nonstandard stellar systems.

Program Type: WTAC

Scheduled Nights:
Run 1 (2017A):  WIYN/HYDR -- 8n on Feb 11 - Feb 14 2017, Jun 02 - Jun 05 2017


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